1. Field of the Invention
The present invention relates to a new and improved means for controlling the change of thickness of lines of photographically produced briefs which are producible by the agency of a means for photographic reproduction.
2. Description of the Prior Art
Recently the graphical art is experiencing an accelerated changing from the use of the leaden printing plate for types or briefs, respectively, to the use of photographically produced briefs. It is a rather easy task to estimate at which point of time in central and western Europe only books of a bibliophilic character will be printed by the agency of leaden printing procedures. The reason for this situation is the fact that the above indicated new technique causes considerable savings on time and space for the graphic business. On the other hand, however, it also produces new technical problems. Specifically the problem regarding the maintenance of quality of a photographically produced brief is vastly different than such of a brief produced by leaden means.
Presently, the composing of a photographically produced brief or document proceeds with the aid of a light source, of a brief storage means (print carrier of a photographically produced brief), a scale or magnitude, respectively means, of a means for setting the distance or gap between characters (letters or types), respectively, and of one or two cassettes for the photographic material.
During the production of photographically produced briefs by means of the projection procedure a light source (incandescent light or flash light) illuminates a negative of a letter or type, respectively, and projects such in the desired scale by the agency of a magnifying optical arrangement onto a photographic material.
During such production by means of beams the light source of the projecting means provided with a guidable cathodic or laser beam composes or assembles the letter or type, respectively, in the desired size linewise or point(dot)-wise on the photographic material. Thereby, it follows a screening program of another light source scanning the negative of the figure, i.e., letter or type. It is, however, also possible to utilize digitally stored information for guiding the printing beam. The illuminated letter or type, respectively, of the brief manufactured by a means of a beam is thus composed of a plurality of lines or dots, respectively, which cannot be individually recognized by the naked eye simply because its capability regarding the resolution does not suffice.
Upon examination of the features which govern the quality of the reproduction of a print two different groups of deficiencies can be detected: A first group encompasses deficiencies regarding the positioning of the letters or types, respectively, a second group encompasses the deformation of the letters or types, respectively. Positioning errors are slanted letters or types, respectively, insufficient maintenance of lines, irregular spacing between letters or types, respectively, and irregular slugs. A deformation of the print involves a flattening of corners combined with a loss of the inner and outer contours, a breaking of or interruption of serifs, a slurred contour and a change of the line thickness.
Undesirable variations of the thickness of the lines result in the individual letter, type, words, lines or complete sections of a text or even pages appearing to be fatter or narrower than intended. Printed matter suffering from such deficiencies appear to be unkempt and furthermore the ease of reading suffers because a reader is not certain if a fatter line is meant to be an intended stressing in the text or if it is due to an unintentional technical deficiency. Thus an avoidance of unwanted changes of the thickness of letters or types, respectively, being beyond the tolerance acceptable by eye is of utmost importance with regard to ensuring the quality of the photographically produced brief.
Changes of the thickness of lines can occur during several production steps: The optical system of the illumination unit of the apparatus for photographically producing briefs can incorporate deficiencies and thus produce irregular results, the light source itself can be subject to variations or changes due to aging which usually immediately brings about a change of the thickness of lines in the brief. Furthermore, the film emulsion used for the photographic production of the brief can feature irregularities or the development of the film can lead to irregular results, which again takes the shape of changes of the thickness of lines. At the copy of the film of the photographically produced brief on the offset printing plate there can also occur changes of the thickness of lines as well as during the following printing step.
In order to measure the changes of the thickness of lines in the photoprint brief there are known generally two methods:
(1) the microscopic measuring method and PA1 (2) the densitometric measuring method.
When following the microscopic measuring method there is utilized a microscope which enlarges 100 times or more and comprises a graduation of 0.01 mm or less. With such instrument the width of the line of letters or type, respectively, can be measured directly. Such method is suitable for detecting the tolerances of the changes of the thickness of lines which still is accepted by the eye of the reader. However, such method is too complicated and bothersome for checking initially set tolerances on a day-by-day production practice. Microscopes having a magnifying power of 1:100 are already laboratory instruments and uncommon to operators for the production of photographic briefs. Thereby, the field of vision is that small that it usually does not even detect a complete letter or type, respectively, which renders the search of suitable measuring areas of the print quite difficult.
The densitometric method is based on the recognition that a broadening of the print and a broadening of the screen dots are due to the same reason and thus can be detected by means of the identical measuring methods. A broadening of the screen dots produces a darker screen area which accordingly produces a higher density value when carrying out a measurement by means of the densitometer.
If now a suitable raster or screen area such as, e.g., a micro measuring area is placed on the print carrier of a photographically produced brief at such place which is usually occupied by a negative of a letter or type, respectively, and furthermore, such screen area is illuminated similar to the illumination of a letter or type, respectively, on a film for the photographic production of a brief this area can upon its development be measured with the aid of a densitometer. Upon a stronger illumination which produces on the one hand an increase of the thickness of lines of the letters or types, respectively, and on the other hand a darkening of the screen or raster area the densitometer will indicate a higher value. Upon a weaker illumination which produces a decrease of the thickness of lines and a brightening of the screen area the densitometer will indicate a lower density value.
Both described measuring methods are suitable for setting standard or base values of the thickness of lines and also for finding the tolerances of the change of the thickness of lines still and just tolerable by the human eye. Thus tolerance values are used for settings such as which are made with the aid of rows of tests.
Such a row of tests can be produced as follows: With regard to a specific letter or type, respectively, form and letter or type, respectively, size there is set by means of tests such thickness of line which produces an optimal picture of the letters or types, respectively, with regard to legibility and appearance. By utilizing the set thickness of line several photographically produced brief blocks are illuminated. Within these brief blocks, however, individual lines are purposely illuminated with varying illumination times such that such lines appear to be fatter or narrower than the rest of the text. Thereafter testing personnel sets the critical change of the intensity of lines at which fatter or narrower ("leaner") letters or types or texts appear to be disturbing for the eye.
The critical change of the thickness of lines, which will be referred to hereafter as tolerance of the thickness of lines, changes to a small extent between type forms and also between sizes of type. Larger sizes of type allow a somewhat larger tolerance of the thickness of lines in comparison with smaller sizes of type. The tolerance of the thickness of lines can be given in terms of micrometers or differences in density for a predetermined screen area.
The nominal value and the tolerance of the intensity of lines can be in accordance with above described methods set for any type form and type size. Because this is an only one time procedure the necessary expenditure of work and time is of no importance. However, it is quite a different task when checking on a day-by-day basis the originally set nominal values and tolerances during the regular production of photographically produced briefs. In such case the above mentioned methods are due to their necessary daily repetition cumbersome.
Accordingly, there is a need in the practice of a means which allows a speedy control of the nominal values and tolerances by utilizing simple devices.